One set of experiments is intended to elucidate role of brain NE, DA, & 5-HT systems in regulation of sympathetic outflow to heart and blood vessels. In neonatal animals the time course for development of CNS tonic and reflex sympathetic regulation of cardiovascular function will be evaluated and the effect of selective interference with CNS NE, DA & 5-HT systems determined. In a second study, the effects of the commonly used antihypertensive agents, propranolol, hydralazine and nitroprusside on sympathetic efferent and baro- and chemoreceptor afferent activity will be studied to elucidate the mechanism of action of these agents.